questions (spoilers included)

-The voice was unexplained. They never said the origin; however, it's implied that its a very powerful and omnipotent human being.
-IDK lol
-Omnipotent and powerful; big brother is always watching lol
-Who knows which challenge that was for the other unknown contestant? That probably wasn't his 13th challenge. Judging by the severity of it, it was probably like challenge 10 or 11.
-There were a lot of people in on it. So chances are the cops were payed some kind of lump sum to keep it quiet. Or they're playing the game too and one of their challenges is to keep it quiet lol many possibilities to that one. But part of the game, is not letting anyone know what your doing. (I think) Why they still dropped the charges after he was disqualified, no idea lol but technically he did complete all the challenges...
"Once upon a time, there was magical place where it never rained. The End."

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How come that grandpa who had WON the game (by killing his wife/lead character's mother), is a poor ass ?? Not a millionaire ....

How did the voice on the phone know everything the contestants were doing at the moment they were doing it?
**They had cameras everywhere and possibly spies who were watching the contestants constantly

-Why did the cell phone suddenly turn into the money counter and score keeper when at first he had to look up his account to see the
deposits?
** The phone always recorded the amount won and challenges completed. Elliott checked it at home only after the first time on his computer to verify the funds were actually transferred.
-How did the voice know what cell numbers to use when our guy stole the phone from a random passerby?
**Again, they were always watching and the "random passerby" could be a plant.

-Why did the voice tell him that he was in a race to get to number 13 before another contestent; then our contestent screwed up the zip line across the road - the other contestant accomplished the challenge - but our guy still won?
**Because Elliott's challenge was to hang the line on the trailer, not necessarily to keep it up. Before he realized the line went across the road the phone dinged with the challenge complete and money deposited. The other guy's challenge was likely that he had to rig up the second line. But since Elliott hadn't gotten another phone call, his next challenge wasn't available yet.
-Why did the cops forget all about our guy - even though he shot the police captain in the foot, and was wanted for multiple felonies, yet he flees the police station buy only a block or so - you can still see the flashing cop cars in the old woman walking down the road scene - but the cops don't go looking for him at all?
**The game makers had loads of money at their disposal and could easily pay off the cops involved and erase his records. The old woman was a plant for the game and the distant flashing lights could just be window dressing to spur Elliott on.

And all records are wiped clean - and even though our guy was disqualified?
**There is only mention of Elliott having his record wiped clean before he shot the cop at the end. Elliott's girlfriend mentioned she called the station earlier but it may have been before he stopped playing the game or got disqualified for interfering. It's likely that the game makers washed their hands of him after he got disqualified and since the evidence wasn't destroyed and the cop was going to be found dead, Elliott is going to be arrested and put away. It's ambiguous though and we don't really know.